Yesterday I upgraded 3 computers (2 ~x86 and 1 ~amd64), and on all of them I see an annoying effect. After starting kde by startx, everything works normally for some unpredictable time (from a few minutes to an hour or so). Then, after no particular action, suddenly, all pull-down menus become just black rectangles (I saw it with firefox and konsole); the kde panel becomes black; all menus and tips prom the panel become black rectangles. If I blindly click on them, they work.
It's very annoying to kill and restart X every 5 minutes. I'm trying to find which upgrade resulted in this behaviour. I've just reverted xf86-video-intel to 2.21.0 and media-libs/mesa to 9.0.1 (which I had before the yesterday's upgrade). No effect, still black rectangles. What else can cause this? upgrades of qt-core and qt-gui? But this bad behaviour also happens for firefox. I don't see any other graphics-related packages in the yesterday's update. But before that everything was normal._________________Andrey Grozin

Have just discovered that not only menus and tooltips are completely black. All new windows created in this regime are black.
Trying to recompile all kde, just out of frustration._________________Andrey Grozin

Did you set eselect qtgraphicsystem to raster? Also check systemsettings > desktop effects > advanced. This setting can get borked through updates easily._________________"Coincidence is God's way of remaining anonymous."
Albert Einstein
"The road to success is always under construction"

Hmm, weird. Other than checking eselect opengl doesn't come to my mind then.
I had to redo KDE configuration from time to time because of some weird stuff... Checking with a new .kde4 directory is worth a shot._________________"Coincidence is God's way of remaining anonymous."
Albert Einstein
"The road to success is always under construction"

i put xfce4 on my machine as rescue mode from gnome3 upgrade problems.... i know its not an ideal solution, but its a temporary fall back to make the machine usable again until further progress is made.